1. Field of the Invention
The present invention relates to a pressure sensor and a method for manufacturing the pressure sensor.
2. Description of Related Art
Conventionally, for pressure measurements and pressure switches of industrial machinery, pressure sensors manufactured according to the MEMS (Micro Electro Mechanical Systems) technique are used. As a pressure sensor, a capacitive detection type pressure sensor which detects a pressure based on an amount of change in capacitor capacity which changes according to an input pressure is known.
FIG. 5 is a schematic sectional view of a conventional pressure sensor.
The pressure sensor 101 includes a silicon substrate 102, a support substrate 103 for supporting the silicon substrate 102, and a sealing substrate 104 for sealing the silicon substrate 102.
On the silicon substrate 102, an upper recess 105 and a lower recess 106 are formed by wet-etching one side (upper side) and the other side (lower side) of the central portion of the silicon substrate in the thickness direction. By forming the upper recess 105 and the lower recess 106, a diaphragm 107 with a thickness smaller than the thickness of the peripheral portion surrounding the central portion (thickness of the silicon substrate 102 main body) is formed at the central portion of the silicon substrate 102. The thickness of the diaphragm 107 allows the diaphragm 107 to oscillate in the thickness direction of the silicon substrate 102.
In an upper layer portion of the diaphragm 107 facing the upper recess 105, a movable electrode 108 capable of oscillating with the diaphragm 107 is formed. The movable electrode 108 is a diffusion electrode provided with conductivity by diffusion of an impurity, and is uniformly formed in the entire region of the upper layer portion of the diaphragm 107.
Also, on the silicon substrate 102, in a region from the side wall of the upper recess 105 to the peripheral portion of the silicon substrate 102, a movable electrode wiring 109 provided with conductivity by diffusion of an impurity is formed to be continuous to the movable electrode 108. The movable electrode wiring 109 is electrically connected to the movable electrode 108.
Also, on the silicon substrate 102, in a region from the side wall of the upper recess 105 to the peripheral portion of the silicon substrate 102, a fixed electrode wiring 110 provided with conductivity by diffusion of an impurity is formed. The fixed electrode wiring 110 is insulated from the movable electrode 108 and the movable electrode wiring 109.
The support substrate 103 is made of, for example, a heat-resistant glass substrate of Pyrex (registered trademark) glass, etc., and is anodically bonded to the silicon substrate 102. In a portion of the support substrate 103 opposed to the diaphragm 107, a through-hole 111 penetrating through the support substrate 103 in the thickness direction is formed.
The sealing substrate 104 is made of, for example, a heat-resistant glass substrate of Pyrex (registered trademark) glass, etc., and is anodically bonded to the silicon substrate 102. Accordingly, a space 112 surrounded by the inner surfaces of the upper recess 105 and the lower surface of the sealing substrate 104 is held in a vacuum state. To the lower surface of the sealing substrate 104, a fixed electrode 113 made of aluminum is fixed opposite to the movable electrode 108. The fixed electrode 113 is electrically connected to the fixed electrode wiring 110 at a position not shown.
In this pressure sensor 101, the movable electrode 108 and the fixed electrode 113 form a capacitor using these as counter electrodes. To this capacitor (between the movable electrode 108 and the fixed electrode 113), a predetermined voltage is applied via the movable electrode wiring 109 and the fixed electrode wiring 110.
In this state, when a pressure (for example, a gas pressure) is input from the through-hole 111, due to an action of the pressure, the movable electrode 108 oscillates with the diaphragm 107, and the capacitance of the capacitor changes. Then, a voltage fluctuation between the movable electrode 108 and the fixed electrode 113 caused by this capacitance change is output as an electric signal.
The sensitivity of the pressure sensor 101 is designed by changing the thickness of the diaphragm 107. Therefore, to manufacture a pressure sensor with a desired sensitivity, the thickness of the diaphragm 107 must be adjusted to a target thickness by properly controlling wet-etching conditions for the silicon substrate 102.
However, the etching rate of the silicon substrate 102 changes with a temperature change of an etchant. Therefore, even when etching conditions are properly controlled, a difference may occur between the thickness of the manufactured diaphragm 107 and the target thickness.